[hermes]

Hi, I am  attempting to grow grafted water melons....so far without success. The plants are thriving and producing small fruit behind the flowers, which swell to about golf ball size before the flower opens. The the fruit change colour and get typical water mellon markings but then slowly loose size, turn black and wither. Is it due to the lack of sunshine or am I doing something wrong. They well watered and given a tomato feed ever two weeks.

[prakash_mib]

any male flowers?
are they pollinating?
are they indoors or outdoors?
thats all I can think of 
location on your profile please so others can give you more specific advice.

[AndyRVTR]

Have you pollunated them with a small brush?

[JayG]

No experience of growing water melons, grafted or otherwise, but what you describe sounds typical of lack of pollination in all cucurbits (with the honourable exception of all-female cucumbers!)

Use a small paintbrush to transfer pollen from the male to the female "naughty bits" to make sure! (Bit worrying though as it's surely getting a bit late for melons?)